1. Field of the Invention
The present invention relates to a mounting structure of a cap and a diaphragm in a speaker device.
2. Description of Related Art
Conventionally, there is known an external-magnet type speaker device including a vibration system having a voice coil bobbin, a diaphragm and a cap having a dustproof function, and a magnetic circuit system having a yokes a magnet and a plate. In such a speaker device, one portion (mounting surface), of an outer peripheral edge portion of the cap is mounted on an area in the vicinity of an outer peripheral edge portion of the diaphragm via an adhesive, and the cap is arranged at a position covering an upper surface of the voice coil bobbin, for example.
There is known a speaker device in which the outer peripheral edge portion of the diaphragm having an upper-side diaphragm and a lower-side diaphragm is mounted onto an inner side edge (see U.S. Pat. No. 6,496,590 and No. 6,501,844, for example). In addition, there is known the speaker device in which the outer peripheral edge portion of a dustproof cap is mounted onto the side of the outer peripheral edge portion of the diaphragm via an adhesive tape (see U.S. Pat. No. 6,639,993, for example). Moreover, there is known the speaker device in which an opening is formed on a pole piece (see U.S. Pat. No. 5,734,734, for example).
However, in the above-mentioned speaker device, a mounting surface (attachment surface) of the cap to the diaphragm is positioned on the side of the outer peripheral edge portion of the cap, and an adhesion area of the cap and the diaphragm is small. Therefore, a vibrating area of the cap at the time of driving of the speaker device is large, and due to the vibration, an abnormal sound (flutter) problematically occurs from the cap. As a method of avoiding such a problem, there is known a method of making the cap thicker so that the vibration of the cap hardly occurs, thereby preventing the occurrence of the abnormal sound (flutter) However, if such a method is employed, the cap becomes heavy by the amount of increased thickness of the cap, and sensitivity of the speaker device decreases as a new problem